The present invention relates to methods of producing an exchange coupling film having an antiferromagnetic layer and a ferromagnetic layer, wherein the direction of magnetization of the ferromagnetic layer is fixed by an exchange coupling magnetic field produced at the interface between the antiferromagnetic layer and the ferromagnetic layer. More particularly, the present invention relates to methods of producing an exchange coupling film that provides a large ratio of resistance variation, to methods of producing a magnetoresistive sensor (spin-valve-type thin-film device, AMR device), and to methods of producing a thin-film magnetic head using the magnetoresistive sensor.
A spin-valve-type thin-film device is a kind of GMR (Giant Magnetoresistive) device which makes use of a giant magnetoresistive effect, which is used for detecting recording magnetic fields from a recording medium such as a hard disk.
The spin-valve-type thin-film device, relative to other GMR devices, has advantageous features such as simplicity of structure and ability to vary its magnetic resistance even under a weak magnetic field.
The simplest form of the spin-valve-type thin-film device includes an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic intermediate layer, and a free magnetic layer.
The antiferromagnetic layer and the pinned magnetic layer are formed in contact with each other. The direction of the pinned magnetic layer is aligned in a single magnetic domain state and fixed by an exchange anisotropic magnetic field produced at the interface between the antiferromagnetic layer and the pinned magnetic layer.
The magnetization of the free magnetic layer is aligned in a direction which intersects the direction of magnetization of the pinned magnetic layer, by the effect of bias layers that are formed on both sides of the free magnetic layer.
Alloy films such as Fexe2x80x94Mn (Iron-Manganese) alloy films, Nixe2x80x94Mn (Nickel-Manganese) alloy films, and Ptxe2x80x94Mn (Platinum-Manganese) alloy films are generally usable materials for the antiferromagnetic layer. Of these, Ptxe2x80x94Mn alloy films are attracting attention for advantages such as a high blocking temperature, superior corrosion resistance, and so forth.
In order to comply with future demand for higher recording density, it is important to achieve greater exchange coupling magnetic fields and greater ratios of resistance variation.
However, it has been impossible to obtain a large ratio of resistance variation with conventional structures of magnetoresistive sensors, which are composed of an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic intermediate layer and a free magnetic layer.
It has been found that the ratio of resistance variation is dependent on exchange coupling magnetic field. The resistance variation ratio decreases unless a large exchange coupling magnetic field is obtained. The resistance variation ratio is also dependent on the crystalline orientations of the layers. It has been heretofore impossible to use conventional structures to obtain a magnetoresistive sensor which possesses both appropriate crystalline orientations and a large exchange magnetic field, and which therefore exhibits a large resistance variation ratio.
Accordingly, an object of the present invention is to provide methods of producing an exchange coupling film in which a seed layer is provided on the side of an antiferromagnetic layer opposite to the interface between the antiferromagnetic layer and the ferromagnetic layer, so as to optimize the crystalline orientations of these layers. Thus, a greater resistance variation ratio than obtained with conventional devices is achieved. Additional objects are to provide methods of producing a magnetoresistive sensor using the exchange coupling film, and methods of producing a thin-film magnetic head using the magnetoresistive sensor. In accord with the present invention, the above-described problems are overcome.
In accord with the present invention, there is provided a method of producing an exchange coupling film comprising an antiferromagnetic layer, a ferromagnetic layer contacting the antiferromagnetic layer at an interface therebetween, and a seed layer comprising a (111) plane of face-centered cubic crystal, which seed layer contacts the antiferromagnetic layer at an interface therebetween on a side opposite the ferromagnetic layer. The method comprises forming the seed layer such that the (111) plane of face-centered cubic crystal is preferentially oriented in a direction parallel to the direction of the interface between the seed layer and the antiferromagnetic layer, while creating a non-aligned state at at least a part of the interface between the antiferromagnetic layer and the seed layer. The method further comprises effecting a heat-treatment after formation of the layers, so as to develop an exchange coupling magnetic field at the interface between the antiferromagnetic layer and the ferromagnetic layer.
As stated above, in accordance with the present invention, a seed layer contacts the antiferromagnetic layer on a side thereof opposite the interface between the antiferromagnetic layer and the ferromagnetic layer. The layer is constituted mainly by a face-centered cubic crystalline structure in which, prior to heat treatment, the (111) plane is preferentially oriented in a direction parallel to the interface. This allows the (111) plane of the antiferromagnetic layer in contact with the seed layer, and the (111) plane of the ferromagnetic layer which, together with the seed layer, sandwiches the antiferromagnetic layer, to be preferentially oriented in a direction parallel to the interface.
It is possible to enhance the resistance variation ratio of a magnetoresistive sensor by using an exchange coupling film in which the (111) planes of the antiferromagnetic layer and the ferromagnetic layer are preferentially oriented, as described above.
The enhancement of the resistance variation ratio requires that a large exchange-coupling magnetic field be developed at the interface between the antiferromagnetic layer and the ferromagnetic layer. In accordance with the present invention, at least a part of the interface between the layers is executed such that a non-aligned state is created at at least a part of the interface between the antiferromagnetic layer and the seed layer. Such a non-aligned state of the interface between the seed layer and the antiferromagnetic layer permits the antiferromagnetic layer to be adequately transformed from a disordered lattice into an ordered lattice upon heat-treatment. As a result, a large exchange coupling magnetic field and, therefore, an enhanced resistance variation ratio can be achieved.
The present invention also provides a method of producing an exchange coupling film comprising an antiferromagnetic layer, a ferromagnetic layer contacting the antiferromagnetic layer at an interface therebetween, and a seed layer comprising a (111) plane of face-centered cubic crystal, which seed layer contacts the antiferromagnetic layer at an interface therebetween on a side opposite the ferromagnetic layer, the method comprising forming the seed layer such that the (111) plane of face-centered cubic crystal is preferentially oriented in a direction parallel to the direction of the interface between the seed layer and the antiferromagnetic layer, while creating a difference in lattice constant between the antiferromagnetic layer and the seed layer at at least a part of the interface therebetween. The method further comprises effecting a heat-treatment after formation of the layers, so that an exchange coupling magnetic field is developed at the interface between the antiferromagnetic layer and the ferromagnetic layer.
In accordance with the present invention, the antiferromagnetic layer and the ferromagnetic layer have different lattice constants at at least a part of the interface between the antiferromagnetic layer and the seed layer. Preferably, a non-aligned state is created at at least a part of the interface between the antiferromagnetic layer and the seed layer. These features make it possible to obtain a large exchange coupling magnetic field and, hence, a large resistance variation ratio.
In accordance with the present invention, the antiferromagnetic layer preferably comprises an element X and Mn, wherein the element X is selected from the group consisting of Pt, Pd, Ir, Rh, Ru, Os, and combinations thereof.
Alternatively, the antiferromagnetic layer may comprise an element X, an element Xxe2x80x2 and Mn, wherein the element X is selected from the group consisting of Pt, Pd, Ir, Rh, Ru, Os, and combinations thereof, while the element Xxe2x80x2 is selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb, a rare earth element, and combinations thereof.
The present invention also provides methods of producing an exchange coupling film comprising an antiferromagnetic layer, a ferromagnetic layer contacting the antiferromagnetic layer at an interface therebetween, and a seed layer comprising a (111) plane of face-centered cubic crystal, which seed layer contacts the antiferromagnetic layer at an interface therebetween on a side opposite the ferromagnetic layer, the method comprising: forming the seed layer such that the (111) plane of face-centered cubic crystal is preferentially oriented in a direction parallel to the interface between the seed layer and the antiferromagnetic layer; depositing on the seed layer an antiferromagnetic layer comprising an element X and Mn, wherein X is selected from the group consisting of Pt, Pd, Ir, Rh, Ru, Os, and combinations thereof; elevating a sputtering gas pressure during the depositing so that a composition ratio (at %) of the element X in the antiferromagnetic layer progressively decreases as distance from the seed layer increases; decreasing the sputtering gas pressure during the depositing so that the composition ratio (at %) of the element X of the antiferromagnetic layer progressively increases as distance from the seed layer further increases; and effecting a heat-treatment after formation of the layers, so as to develop an exchange coupling magnetic field at the interface between the antiferromagnetic layer and the ferromagnetic layer.
The present invention also provides a method of producing an exchange coupling film comprising an antiferromagnetic layer, a ferromagnetic layer contacting the antiferromagnetic layer at an interface therebetween, and a seed layer comprising a (111) plane of face-centered cubic crystal, which seed layer contacts the antiferromagnetic layer at an interface therebetween on a side opposite to ferromagnetic layer, the method comprising: forming the seed layer such that the (111) plane of face-centered cubic crystal is preferentially oriented in a direction parallel to the interface between the seed layer and the antiferromagnetic layer; depositing on the seed layer an antiferromagnetic layer comprising an element X, an element Xxe2x80x2 and Mn, wherein X is selected from the group consisting of Pt, Pd, Ir, Rh, Ru, Os, and combinations thereof, and Xxe2x80x2 is selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Go, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb, a rare earth element, and combinations thereof; elevating a sputtering gas pressure during the depositing so that a composition ratio (at %) of the elements X+Xxe2x80x2 of the antiferromagnetic layer progressively decreases as distance from the seed layer increases; decreasing the sputtering gas pressure during the depositing so that the composition ratio (at %) of the elements X+Xxe2x80x2 of the antiferromagnetic layer progressively increases as distance from the seed layer further increases; and effecting a heat-treatment after formation of the layers, so as to develop an exchange coupling magnetic field at the interface between the antiferromagnetic layer and the ferromagnetic layer.
According to this method of the present invention, a portion of a composition prone to order transformation is formed near the middle of the antiferromagnetic layer. The antiferromagnetic layer is formed such that the composition of the antiferromagnetic layer at the interface between the seed layer and the antiferromagnetic layer is not constrained by factors such as the crystalline structure of the seed layer.
In these methods of the present invention, the composition ratio of the element X or the composition ratio of the elements X+Xxe2x80x2 of the antiferromagnetic layer to the total composition ratio (100 at %) of all the elements constituting the antiferromagnetic layer is not less than 53 at % and not more than 65 at %, preferably not less than 55 at % and not more than 60 at %, in a region near the interface between the antiferromagnetic layer and the ferromagnetic layer, and in a region near the interface between the antiferromagnetic layer and the seed layer.
In these methods of the present invention, it is also preferred that the composition ratio of the element X or the composition ratio of the elements X+Xxe2x80x2 is not less than 44 at % and not more than 57 at %, more preferably not less than 46 at % and not more than 55 at %, in a region near the thicknesswise central portion of the antiferromagnetic layer.
Preferably, the antiferromagnetic layer is formed to have a thickness of 76 xc3x85 or greater.
The present invention also provides a method of producing an exchange coupling film comprising an antiferromagnetic layer, a ferromagnetic layer contacting the antiferromagnetic layer at an interface therebetween, and a seed layer comprising a (111) plane of face-centered cubic crystal, which seed layer contacts the antiferromagnetic layer at an interface therebetween on a side opposite to the ferromagnetic layer, the antiferromagnetic layer comprising a first antiferromagnetic layer, a second antiferromagnetic layer, and a third antiferromagnetic layer, the method comprising: forming the seed layer such that the (111) plane of face-centered cubic crystal is preferentially oriented in a direction parallel to the interface between the seed layer and the antiferromagnetic layer; forming the antiferromagnetic layer such that the third antiferromagnetic layer is adjacent to the seed layer, the first antiferromagnetic layer is adjacent to the ferromagnetic layer, and the second antiferromagnetic layer is between the first and third antiferromagnetic layers, wherein each of the first, the second, and the third antiferromagnetic layers comprises an element X and Mn, wherein X is selected from the group consisting of Pt, Pd, Ir, Rh, Ru, Os, and combinations thereof, such that the second antiferromagnetic layer has a smaller composition ratio of the element X than the first and the third antiferromagnetic layers; and effecting a heat-treatment after formation of the layers, such that an exchange coupling magnetic field is developed at the interface between the antiferromagnetic layer and the ferromagnetic layer.
In this method of the present invention, the first, second and third antiferromagnetic layers may be formed from antiferromagnetic materials comprising an element X, an element Xxe2x80x2 and Mn, wherein the element Xxe2x80x2 is selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb, a rare earth element, and combinations thereof.
In this method of the present invention, the antiferromagnetic layer is composed of a triple-layer laminate. During deposition of the third antiferromagnetic layer, the composition ratio of the element X in the third antiferromagnetic layer is set to be greater than that of the second antiferromagnetic layer so that, at the interface between the third antiferromagnetic layer and the seed layer, the restraint force produced by the crystalline structure of the seed layer is weakened. As a result, a non-aligned state or a different lattice constant is obtained, thereby facilitating transformation of the antiferromagnetic layer to an ordered lattice upon heat-treatment without influence from the crystalline structure of the seed layer. As a result, a greater exchange coupling magnetic field is obtained than heretofore.
Setting the composition ratio of the element X in the second antiferromagnetic layer to a value smaller than in the first and third antiferromagnetic layers facilitates transformation of the second antiferromagnetic layer upon heat-treatment. This in turn promotes transformation of the whole antiferromagnetic layer through a diffusion of the composition, whereby a large exchange coupling magnetic field is obtained.
In accordance with the present invention, the antiferromagnetic layer and the seed layer may have different lattice constants at at least a part of the interface therebetween. Preferably, in accord with the present invention, a non-aligned state is created at at least a part of the interface between the antiferromagnetic layer and the seed layer.
When the above-mentioned Xxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy is used as the material of the antiferromagnetic layer, it is preferred that the element Xxe2x80x2 is an element which either invades the interstices of a space lattice composed of the element X and Mn, or substitutes for a portion of the lattice points of a crystalline lattice constituted by Mn and the element X.
In accordance with the present invention, the composition ratio of the element X or the composition ratio of the elements X+Xxe2x80x2 of each of the first and third antiferromagnetic layers is preferably not less than 53 at % and not more than 65 at %, more preferably not less than 55 at % and not more than 60 at %.
In accordance with the present invention, it is also preferred that the composition ratio of the element X or the composition ratio of the elements X+Xxe2x80x2 of the second antiferromagnetic layer is not less than 44 at % and not more than 57 at %, more preferably not less than 46 at % but not more than 55 at %.
In accordance with the present invention, it is preferred that each of the first and third antiferromagnetic layers has a thickness not smaller than 3 xc3x85 and not greater than 30 xc3x85.
In accordance with the present invention, it is also preferred that the second antiferromagnetic layer has a thickness of 70 xc3x85 or greater.
In accordance with the present invention, it is preferred that the antiferromagnetic layer and the ferromagnetic layer have different lattice constants at at least a part of the interface therebetween. In addition, it is preferred that a non-aligned state is created at at least a part of the above-mentioned interface. With these features, an appropriate ordered transformation of the entire antiferromagnetic layer is facilitated.
In accordance with the present invention, it is preferred that the seed layer is formed of a Nixe2x80x94Fe alloy or a Nixe2x80x94Fexe2x80x94Y alloy, wherein Y is selected from the group consisting of Cr, Rh, Ta, Hf, Nb, Zr, Ti, and combinations thereof.
It is also preferred that the seed layer is non-magnetic. The non-magnetic nature of the seed layer serves to enhance the specific resistance of the seed layer, so that shunting of a sense current to the seed layer is suppressed. As a result, greater resistance variation ratio in the exchange coupling film obtained after heat-treatment is obtained.
In accordance with the present invention, it is preferred that the exchange coupling film is formed by sequentially depositing a seed layer, an antiferromagnetic layer, and a ferromagnetic layer on an underlying layer, wherein the underlying layer comprises an element selected from the group consisting of Ta, Hf, Nb, Zr, Ti, Mo, W, and combinations thereof.
This facilitates formation of a seed layer having a crystalline structure constituted mainly by face-centered cubic crystals with the (111) plane preferentially oriented in a direction parallel to the above-mentioned interface.
The methods of producing an exchange coupling film described hereinabove can be used for the production of a variety of types of magnetoresistive sensors.
In accordance with the present invention, there is provided a method of producing a magnetoresistive sensor comprising an antiferromagnetic layer, a seed layer contacting the antiferromagnetic layer at an interface therebetween, a pinned magnetic layer contacting the antiferromagnetic layer at an interface therebetween which has a direction of magnetization fixed by an exchange anisotropic magnetic field with the antiferromagnetic layer, a non-magnetic intermediate layer between the pinned magnetic layer and a free magnetic layer, and a bias layer which aligns a direction of magnetization of the free magnetic layer in a direction that intersects the direction of magnetization of the pinned magnetic layer, the method comprising forming the antiferromagnetic layer, the pinned magnetic layer, and the seed layer by one of the methods described hereinabove.
In accordance with the present invention, there is provided a method of producing a magnetoresistive sensor comprising an antiferromagnetic layer, a seed layer contacting the antiferromagnetic layer at an interface therebetween, a pinned magnetic layer contacting the antiferromagnetic layer at an interface therebetween which has a direction of magnetization fixed by an exchange anisotropic magnetic field with the antiferromagnetic layer, a non-magnetic intermediate layer between the pinned magnetic layer and a free magnetic layer having an upper side and a lower side, and an antiferromagnetic exchange bias layer formed on either the upper side or the lower side of the free magnetic layer, the antiferromagnetic exchange bias layer comprising at least one gap in the track width direction, the method comprising: forming the exchange bias layer, the free magnetic layer and the seed layer by one of the methods described hereinabove.
The present invention also provides a method of producing a magnetoresistive sensor comprising a seed layer; a first antiferromagnetic layer overlying the seed layer; a first pinned magnetic layer overlying the first antiferromagnetic layer; a first non-magnetic layer overlying the first pinned magnetic layer; a free magnetic layer overlying the first non-magnetic layer, the free magnetic layer having an upper side and a lower side; a second non-magnetic layer overlying the free magnetic layer; a second pinned magnetic layer overlying the second non-magnetic layer; a second antiferromagnetic layer overlying the second pinned magnetic layer, the first and second antiferromagnetic layers serving to fix directions of magnetization of the first and the second pinned magnetic layers by exchange an isotropic magnetic fields; and a bias layer which aligns a direction of magnetization of the free magnetic layer to a direction that intersects the directions of the first and the second pinned magnetic layers, the method comprising: forming at least one of the first and the second antiferromagnetic layers, at least one of the first and the second pinned magnetic layers, the seed layer, and at least one of the lower side and the upper side of the free magnetic layer, by one of the methods described hereinabove.
The present invention also provides a method of producing a magnetoresistive sensor comprising a magnetoresistive layer having an upper side and a lower side and a soft magnetic layer, the magnetoresistive layer and the soft magnetic layer being superposed through the intermediacy of a non-magnetic layer, an antiferromagnetic layer on the upper side or the lower side of the magnetoresistive layer, the antiferromagnetic layer comprising at least one gap in the track width direction, and a seed layer contacting the antiferromagnetic layer, the method comprising the forming the antiferromagnetic layer, the magnetoresistive layer and the seed layer by one of the methods described hereinabove.
A method for producing a thin-film magnetic head in accord with the present invention comprises forming a shield layer across the gap layer, on each of the upper side and the lower side of a magnetoresistive sensor produced by one of the methods described hereinabove.